Coordinating with owner’s consultants is a basic service (B101, 3.1.2). The owner’s consultants (civil and landscaping) are designing the outside of the building, and the architect must coordinate with them to, for example, make sure the front door elevation is at the proper height. There’s no additional fee for this.
‘Coordinating the owner’s consultants’ is a supplemental service - this goes a step beyond what’s described above. This means taking on the administration of those consultant’s contracts - their schedule, paying them, etc. That’s what 4.1.1.20 is talking about. The architect takes on additional liability by doing this - they’re now responsible if the consultant doesn’t perform according to the contract, if they require additional fees to complete their scope of work, etc. That’s what the additional fee covers.